Field of the Invention
The present invention relates to the technical field of magnetic resonance imaging, in particular a method and device for checking a body coil of a magnetic resonance imaging system.
Description of the Prior Art
Magnetic resonance imaging (MRI) is a technology in which the phenomenon of magnetic resonance is utilized for the purpose of imaging. The basic principles of magnetic resonance are as follows. When an atomic nucleus contains a single proton, as is the case with the nuclei of the hydrogen atoms that are present throughout the human body, this proton exhibits spin motion and resembles a small magnet. Moreover, the spin axes of these small magnets lack a definite pattern, but when an external magnetic field is applied, the small magnets will be rearranged according to the magnetic force lines of the external magnetic field. Specifically, they will align in two directions, either parallel or anti-parallel to the magnetic force lines of the external magnetic field. The direction parallel to the magnetic force lines of the external magnetic field is called the positive longitudinal axis, while the direction anti-parallel to the magnetic force lines of the external magnetic field is called the negative longitudinal axis. The atomic nuclei only have a longitudinal magnetization component, which has both a direction and a magnitude. A radio frequency (RF) pulse of a specific frequency is used to excite the atomic nuclei in the external magnetic field such that their spin axes deviate from the positive longitudinal axis or negative longitudinal axis, giving rise to resonance—this is the phenomenon of magnetic resonance. Once the spin axes of the excited atomic nuclei have deviated from the positive or negative longitudinal axis, the atomic nuclei have a transverse magnetization component.
Once emission of the RF pulse has ended, the excited atomic nuclei emit an echo signal, gradually releasing the absorbed energy in the form of electromagnetic waves, such that their phase and energy level both return to the pre-excitation state. An image can be reconstructed by subjecting the echo signal emitted by atomic nuclei to further processing, such as spatial encoding.
In an MRI system, a body coil (BC) may develop an error due to a fault in e.g. a capacitor, PIN diode or PCB. When this error is not large, it cannot be detected by the MRI system, so the scanner will not stop operation because of such an error. However, an adjustment value of a BC with such an error may be different from the required value, and the scanning result will be affected.
In an MRI system, a maintenance engineer conducts a comprehensive check of the state of a BC by periodic quality inspections. If an error is found during such an inspection, the maintenance engineer will resolve the issue. Thus, in order to ensure that the MRI system is always in a normal operating state, the maintenance engineer must visit the site periodically (e.g. once every 6 months).
Specifically, the quality inspection items include: 1) BC tuning inspection: the maintenance engineer uses a device similar to a network analyzer to conduct a comprehensive scan of the system operating band, and any error in the BC can be detected by means of this tuning inspection; 2) BC coupling parameters; 3) coil transmission efficiency: the maintenance engineer uses a dedicated phantom setting to perform normal transmission adjustment; BC efficiency can be indicated by a coil power loss, which can be derived from a transmission adjustment result. However, quality inspection items need many items of hardware and software support, and cannot be implemented automatically during normal scanning by the system.